Foundry mold and core and composition therefor



- the foundry mold and non-porous that cracks are Patented Dec. 8, 1942 PATENT 'OFFICIE FOUNDRY MOLD AND CORE CODIPOSITION THEREFOR Donald S. Hake and Wilbur G.

Falls,

Manufacturing Company.

corporation 'of Maine No Drawing. Application April 24, '1941,

Serial No. 390,126

/ 8 Claims. (01. 22-l88') This invention relates to acomposition for foundry molds or cores.

More particularly, it

relates to such a composition containing zircon or other refractory zirconium compound as its principal ingredient.

In the art of casting metals, 'both ferrous and non-ferrous, into sand molds or aroundsand cores, foundrymen are consistently having trouble' with the burning in" of the sand to castings. The reason for this distressing problem is that ordinary foundry silica sand is not refractory enough to withstand the hot molten metal without some degree of fusion of the foundrysilica sand. This fused sand becomes entangled in the molten iron along the walls of the molds and cores, which makes a very rough surface on the castings when they become cold enough'to' be shaken out of the sand. This rough surface on the castings must be cleaned by sand blasting, and very often by chipping, thereby increasing the cost of the casting. The

embedded fused sand, if not removed entirely,

destroys the cutting edge of machine tools when the castings are being machined to precision size.

In order to overcome this difflculty, it has been suggested to employ refractory zirconium compounds, particularly zircon, instead of silica as material or mold lining, as described in Bensing' Patent No. 1,886,249. With this material, however, an additional difllculty becomes apparent. The zircon sand does not "burn in" the casting, but the iron in the casting has a tendency to penetrate the mold or core sand, forming deposits of iron oxide therein. In other words, the casting material penetrates the mold, instead of the mold material penetrating the casting.

In copending' application to Wellings and Hake, Serial No. 368,228, filed December 2, 1940, there is described and claimed one method for overcoming these dimculties, by providinga' coating or lining for foundry mold and core sands either of silica or zircon with a composition containing finely divided zircon and carbon. Sometimes, however, it is desirable to form molds or cores without any lining or facing, particularly for hollow castings where cores of small sizeare used. Under these circumstances, a mixture of finely divided zircon and carbon cannot be used because the material becomes so dense, tight very likely to occur and gases evolved during casting and cooling have no opportunity to escape.

In handling any of the materials used for foundry mold purposes, it is customary to pre- Welllngs, Niagara New York, N. Y., a

pare suitable molding mixtures at a central plant or factory, and then ship such mixtures to the various foundries. Most of the foundries are relatively small in size and are not equipped to prepare molding mixtures on an economical scale. Accordingly, it is desirable to prepare solid mixtures which can be conveniently shipped from place to place, and to which the foundryman need add only small quantities of liquids to bind the particles of the mixture together in the shape of a relatively coherent mold or core.

In accordance with the present invention, a foundry mold or core material is provided comprising a major proportion of granular zircon or zircon sand or otherrefractory zirconium compound and a minor proportion of granular carbon or coke, preferably with less than part of,

over long distances the jarring and agitation of the mixture during shipment causes the heavier zircon to settle to the bottom- This difliculty is overcome by incorporating in the mixture a very small percentage of a core oil, sufllcient to prevent this settling but insuflicient to cause binding of the mixture. It has been found that any amount of core oil in excess of about of 1% causes binding. The best quantity, in fact, is about A part of core oil 'per 100 parts of zircon. With this quantity no settling occurs and at the same time the mixture can be easily molded into the required shape at the foundry. Quantities from 0.1 to part are suitable.

Under the term core oil is meant to'be included oils which are commonly used as binders for foundry mold sands and molding compositions. Oils which are suitable are linseed oil, rosin oil, and others.

In the practice of the present invention, the carbon serves to prevent penetration of the mold or core by iron oxide. It apparently acts by maintaining a reducing medium. The quantity of carbon included should be from 1 to 50 parts per 100 parts of zircon or other refractory zirconium compound. A suitable quantity has been found to be about 10 parts. The carbon, like the zircon, should a granular material having particle sizes approximately the same as the granular zircon. Attempts to use finely divided or milled carbon have been unsuccessful. A con' rated with the granular zircon or zircon sand a mesh. Granular coke of 35 to 120 mesh is also suitable.

Although zircon is the preferred zirconium compound for use in the practice of this inven-- tion, because of its relative cheapness and abundance, other refractory zirconium compounds may also be used. Examples of these are: natural or crude baddeleyite, which is mainly zirconium oxide; synthetic baddeleyite; and other forms of synthetic zirconium oxide.

When the material according to the present invention is used in a foundry, it is mixed with a small quantity such as 1 /2% of a core oil, 1V2% of water, and 1 to 172% of a solid binder, such as a cereal binder or a colloidal clay of the nature of bentonite. This is molded into the required shape, and is then ready for casting a molten metal thereinto, or forming cores forsuch castings.

When parts are mentioned parts by weight are understood.

As many variations are possible within the scope of this invention, it is not intended to be limited except as defined by the appended claims.

We claim:

1. A composition for foundry molds and cores comprising 100 parts of a granular refractory zirconium compound and 1 to 50 parts of gran-' ular carbon. I

2. A composition for foundry molds and cores comprising 100 parts of granular zircon and 1 to 50 parts of granular carbon.

3. A composition for foundry molds and cores comprising 100 parts of a granular refractory zirconium compound, 1 to 50 parts of granular coke, and 0.1 to 0.75 part of a core oil.

4. A composition for foundry molds and cores comprising 100 parts of granular zircon, 1 to 50 parts of granular coke, and 0.1 to 0.75 part of a core oil. p

5. A composition for foundry molds and cores comprising 100 parts of granular zircon, about 10 parts of granular coke, and about 0.75 part of a core oil.

6. A foundry mold comprising a mixture of -l00 parts of a granular refractory zirconium 

